In the past, the only types of dispenser for liquid to semi-solid substances in which an air vacuum has been established have comprised a rigid container (such as a glass flask or a metal can) associated with a dispenser member, which member is of the valve type. The corresponding packaging method includes a stage during which the air remaining in the full container is sucked out between the neck of the container and the valve which has been placed thereon but is not yet fixed in place. This has the effect of establishing reduced pressure inside the container while the valve bears hermetically against the neck. A subsequent stage consists in fixing the valve definitively to the neck (by crimping inwards or outwards, . . . ) and this may be done at any moment after suction has been completed. This method is used essentially with dispensers that are maintained under pressure by means of a propellant gas. The temporary vacuum established inside the container serves to leave room for the propellant gas without giving rise to significant excess pressure. The propellant gas is then inserted via the valve that has been fixed on the container.
This prior art method is not suitable for use with variable capacity containers associated with "airless" pumps, i.e. pumps that prevent ingress of air. For example, if the container is a flexible pouch, the suction would have the effect of deforming the container and removing some of the substance. And since the inside of the container remains at atmospheric pressure, the dispenser member would not bear against the neck adequately for sealing purposes. As a result, shortly after suction has ceased, air would get back into the container which would return to its original shape.
Nevertheless prior art methods could be used, providing the dispenser member is fixed in place very quickly after the air has been removed. However, under such circumstances the initial content of the dispenser made in this way is less than the maximum possible capacity of the container. This is because, in practice, some substance is always removed together with the air insofar as it is not possible to adjust the period during which suction is maintained finely. In other words the container is over dimensioned, thereby increasing the cost of the dispenser. The resulting economic loss is particularly perceptible since mass production is generally involved.
An object of the present invention is therefore to provide a method of establishing an air vacuum in a variable capacity container filled with a substance which may be liquid to semi-solid and of fixing a dispenser member thereon without allowing air to get back into the container while the dispenser member is being fixed, while nevertheless maintaining the maximum capacity of the container.